Statistical Physics Seminar

Tuesday, February 29, 2000, 1:15 p.m.
IPST Building, Room 1116

Quantum superconductor-insulator phase transition in ultrathin nanowires

Alexey Bezryadin

(Harvard University)

Abstract:  The phenomenon of superconductivity depends on the coherence of the phase of the condensate. For small systems, such as Josephson junctions or ultrathin wires, the phase is a quantum variable which may or may not have a definite value, corresponding to superconducting and insulating states respectively. To study these quantum effects in quasi-one-dimensional superconductors we have developed a new technique which allows fabrication of uniform nanowires down to ~5 nm in diameter. This is below the resolution limit of modern electron beam lithography. Measurements on nanowires of different sizes show that the insulating state does exist -- it occurs in wires which have their normal-state resistance higher than the quantum resistance for Cooper pairs. A superconducting state is recovered when the "friction", given by the normal conductance of the wire, is strong enough to suppress tunneling of phase slips.

Host: Ellen Williams

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